The design, synthesis and study of nanocomposite materials comprising magnetic nanoparticles embedded in a non-magnetic “host matrix” have attracted significant interest over the last decade. Magnetic nanoparticles can include one or more of the following: para- , superpara- , and ferro-magnetic particles. In this regard, a “nanocomposite” material is a material comprising nanoparticles embedded in, suspended in, or otherwise structurally associated with a different “host material,” such as an organic polymer. An important group of these materials includes magneto-optic (MO) nanocomposites, which exhibit magneto-optical behavior under defined conditions. For example, MO properties of composites comprising Fe, Co, γ-Fe2O3, Fe3O4, or CoFe2O4 nanoparticles in various host materials such as any of various organic polymers, silica gels, colloidal silica particles, glass, or ion-exchange resins have been previously reported.
Examples of MO nanocomposites comprising Fe, Co, γ-Fe2O3, Fe3O4, or CoFe2O4 nanoparticles are discussed in these respective publications: Gonsalves et al., “Magneto-optical Properties of Nanostructured Iron,” J. Materials. Chem., Vol. 7, No. 5, pp. 703-704 (1997); Kalska et al., “Magneto-optics of Thin Magnetic Films Composed of Co Nanoparticles,” J. Appl. Phys., Vol. 92, page 7481 (2002); Guerrero et al., “Faraday Rotation in Magnetic γ-Fe2O3/SiO2 Nanocomposites,” Appl. Phys. Lett., Vol. 71, No. 18, pp. 2698-2700 (1997); Barnakov et al., “Spectral Dependence of Faraday Rotation in Magnetite-Polymer Nanocomposites,” J. Phys. Chem. Solids., Vol. 65, No. 5, pp. 1005-1010 (2004); and Stichauer et al., “Optical and Magneto-optical Properties of Nanocrystalline Cobalt Ferrite Films,” J. Appl. Phys., Vol. 79, No. 7, pp. 3645-3650 (1996). Examples of MO nanocomposites in which the host material is an organic polymer and an ion-exchange resin may be found in these respective publications: Smith et al., “Magneto-optical Spectra of Closely Spaced Magnetite Nanoparticles,” J. Appl. Phys., Vol. 97, pp. 10M504-01-10M504-3 (2005) and Ziolo et al. “Matrix-Mediated Synthesis of Nanocrystalline γ-Fe2O3: A New Optically Transparent Magnetic Material,” Science, Vol. 257, No. 5067, pp. 219-223 (1992).
MO nanocomposites offer possibilities of exploiting the magnetic and/or optical properties of the nanoparticles and the processability of the host material. MO-active nanocomposites offer tantalizing prospects for use in magnetic field sensors, integrable optical isolators, polarizers, and rotators, high-speed MO modulators, and information storage (e.g., as used in data-storage devices comprising MO-active nanocomposite media).
For example, a composite of γ-Fe2O3 nanoparticles in an organic resin absorbs less incident electromagnetic radiation than bulk γ-Fe2O3 particles. Ziolo et al., “Matrix-Mediated Synthesis of Nanocrystalline γ-Fe2O3: A New Optically Transparent Magnetic Material,” Science, Vol. 257, No. 5067, pp. 219-223 (1992). Also, Fe nanoparticles suspended in a matrix material produce a larger MO effect than the bulk Fe particles, and the magnitude of the MO effect appears to be dependent both on particle density and the characteristics of particle/host material interface. Sepulveda et al., “Linear and Quadratic Magneto-optical Kerr Effects in Continuous and Granular Ultrathin Monocrystalline Fe Films,” Phys. Rev. B, Vol. 68, page 064401 (2003), and Jiang et al., “Magnetooptical Kerr Effect in Fe—SiO Granular Films,” J. Appl. Phys., Vol. 78, No. 1, pp. 439-441 (1995).
Although the properties of isolated single-domain magnetic nanoparticles are relatively well understood, the competition between single-particle responses and correlation effects produced by nanocomposites of such particles continues to be an area of intense research. One challenge in assembling a magnetic nanocomposite material is achieving a uniform dispersion of the nanoparticles in the host material with minimal clustering of the magnetic nanoparticles. Even ambient magnetic fields, such as that of the Earth, encourage formation of aggregates of magnetic nanoparticles whenever they are free to move about. Rigidification of the host material inhibits migration and aggregation of the nanoparticles. But, many problems remain with conventional methods for producing nanocomposite materials, especially such materials having particular functional properties. In view of the foregoing, there is a need for improved methods for producing nanocomposites, including MO nanocomposites, without producing unwanted aggregations and/or clusters of the nanoparticles, and that allow reliable production of nanocomposites having one or more target properties.